This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 arising from an application entitled, METHOD FOR REGISTERING THE LOCATION OF A MOBILE STATION AFTER PERFORMING INTER-MSC SOFTHANDOFF IN A CELLULAR, earlier filed in the Korean Industrial Property Office on Aug. 27, 1998, and there duly assigned Serial No. 1998-34784.
The present invention relates to a method for registering the location of a mobile station after performing inter-mobile switching centers (MSCs) soft handoff in a cellular system using code division multiple access (CDMA) technology. Particularly, it is related to a method for detecting the location information of the mobile station by the MSC after the inter-MSC soft handoff is performed in a cellular system.
The cellular system divides the entire service area into a plurality of the base station areas (i.e., cells) and the base stations are controlled by a mobile switching center (MSC). It is not unusual that a subscriber of a mobile telephone (MT) system makes a call while traveling between cells.
In the cellular system, when a mobile telephone (MT) moves from one cell area into another, the call connection is maintained by a handoff between mobile switching centers (MSCs). The handoff occurs when the system recognizes that the MT has moved from a previously identified cell area into another cell area.
FIG. 1 is an exemplary block diagram showing an inter-MSC handoff procedure according to the prior art. As shown in FIG. 1, when an MT (10) moves from a cell area of base transceiver station (BTS) 1 (20), which belongs to a MSC 1 (30), to another cell area of base transceiver station (BTS) 2 (50), which belongs to a MSC 2 (40), an inter-MSC handoff must occur.
When an inter-MSC handoff occurs, it is impossible to exchange the information which is necessary for a smooth handoff because the base transceiver stations 1 and 2 belong to different respective MSCs. Instead, the MT performs a hard handoff by cutting off the channel of the base station (BTS) 1 and connecting to the channel of the base station (BTS) 2. However, such a hard handoff may degrade the call quality.
An improved prior art CDMA system provides an inter-MSC soft handoff using a router for connecting two base transceiver stations, which belong to the different respective MSCs. A soft handoff is a method for connecting a MT with two or more base transceiver stations at the same time. The MT selects the strongest signal among all of the signals received from the plurality of base transceiver stations, and then demodulates it. This multiple reception permits the base transceiver stations connected with the MT to exchange the necessary information about a call with each other.
FIG. 2 is an exemplary block diagram showing the inter-MSC handoff procedure according to the prior art. As shown in the figure, a cellular system providing an inter-MSC soft handoff connects the two base transceiver stations (BTSs) (20) (50) via routers (60) (70), wherein the two base transceiver stations (20) (50) belong to the different respective MSCs. The two routers are connected via relay line (1).
After the MT (10) initially establishes a call with the BTS 1 (20), should the MT (10) move into the area of BTS 2 (50), then BTS 1 (20) requests a soft handoff to BTS 2 (50) via the routers (60) (70). If the soft handoff is made, the BTS 1 (20) selects the best (strongest) received signal from among the signal directly from the MT and the signal received via BTS 2 (50) and routers (60) (70), which is then transmitted to the MSC 1 (30). The MSC 1 (30) transmits the received signal from the base station 1 (20) to the called side.
Through the procedure described in the above, the MT is able to connect the channel with the BTS 1 (20) and the base station 2 (50) at the same time, wherein the two BTSs (50) belong to the different respective MSCs.
As described above, in the case where the MT performs a call through the inter-MSC soft handoff, the two MSCs (30) (40) do not know the present location of the MT (10) (i.e., the cell servicing area of the BTS in which the MT (10) is presently located) because the MT (10) is moving the between boundary area of the two BTSs (20) (50).
During a busy state, the MT can connect its channel with the two BTSs at the same time via soft handoff. However, when the MT is in an idle state it is synchronized only with a single BTS.
If the MT (10) is located within a servicing area of BTS 2 (50), and a call is completed, the BTS 1 (20) reports to the MSC 1 (30) the information about the handoff completion because BTS 1 (20) was the base station originally connected to the MT 10 and the MSC 1 (30). However, an error occurs about the location of the MT (10) because in reality the MT (10) is actually synchronized with BTS 2 (50) in the area of the MSC 2 (40).
Accordingly, in the prior art, in the case where there is a first MSC in which the MT is located and a second MSC which was notified with the information about the completion of the handoff, if the first and second MSCs are different, the first MSC doesn""t transmit the location information about the completion of the first MSC handoff to the second MSC in which the MT is now located. When a call is completed after an inter-MSC soft handoff has occurred and if a called signal arrives at the MT, then other MSC cannot process the called signal.
According to a first preferred embodiment of the present invention, a method for registering the location of a mobile station after performing an inter-MSC soft handoff in a cellular system, wherein the cellular system has a plurality of base transceiver stations (BTSs) and a plurality of the MSCs, and in which the plurality of BTSs provide mobile communication service to the mobile stations in a specific area, said method comprising the steps of:
(a) performing an inter-MSC soft handoff according to the movement of a mobile station from a first BTS in service to at least a second BTS which is controlled by a different MSC than said first BTS;
(b) synchronizing the mobile station with a BTS from among said plurality of BTSs so that said synchronized BTS has a strongest pilot signal after normal completion of a call;
(c) ordering said mobile station to register a location of said mobile station with said synchronized BTS; and
(d) performing a location registration of said mobile station to an MSC controlling said synchronized BTS with the registered location of said mobile station registered in step (c).
According to the first embodiment, it is preferable that the inter-MSC soft handoff performed is performed with the use of a router; the router connects the two neighboring BTSs, the two BTSs are controlled by different respective MSCs.
According to the first embodiment, it is preferable that a first BTS, which is initially connected to the MSC, receives the necessary information after call completion, not through the MSC to which the first BTS belongs, but from a second BTS corresponding to the inter-MSC handoff through the router and other controls of the inter-MSC soft handoff.
According to a second preferred embodiment of the present invention, a method for registering the location of a mobile station after performing inter-MSC soft handoff in a cellular system, wherein the cellular system has a plurality of base transceiver stations (BTSs) and a plurality of the MSCs, and in which the plurality of BTSs provide the mobile communication service to the mobile stations in a specific area, said method comprising the steps of:
(a) performing an inter-MSC soft handoff according to the movement of a mobile station from a first BTS in service to at least another BTS which is controlled by an MSC other than an MSC which controls said first BTS;
(b) said mobile station abnormally completing the call after performing said inter-MSC soft handoff;
(c) synchronizing said mobile station with a BTS having the strongest pilot signal;
(d) ordering said mobile station to register a location of said mobile station with said synchronized BTS having the strongest pilot signal; and
(e) performing a location registration to an MSC controlling said synchronized BTS with the registered location of said mobile station registered in step (d).
According to the second embodiment, it is preferable in the embodiment that the inter-MSC soft handoff is performed by using a router, and the router connects the two neighboring BTSs, and the two BTSs controlled by different respective MSCs.
According to the second embodiment, it is preferable that a BTS initially connected to the MSC receives the necessary information from a BTS corresponding to the inter-MSC handoff through the router and other controls of the inter-MSC soft handoff, and not through an MSC to which the BTS belongs.
According to a third preferred embodiment of the present invention, a method for registering the location of a mobile station after performing inter-MSC soft handoff in a cellular system, wherein the cellular system has a plurality of base transceiver stations (BTSs) and a plurality of the MSCs, and in which the plurality of BTSs provide the mobile communication service to the mobile stations in a specific area, said method comprising the steps of:
(a) performing an inter-MSC soft handoff according to the movement of a mobile station from a first BTS in service to at least one other BTS which is controlled by an MSC other than the MSC controlling said first BTS;
(b) updating the status of said mobile station to idle state after said inter-MSC soft handoff and completion of the call by said mobile station;
(c) synchronizing said mobile station in the idle state with any one of a plurality of neighboring BTSs to said mobile station; and
d) performing a location registration of said mobile station to an MSC controlling said synchronized BTS through said synchronized BTS.
According to the third embodiment, it is preferable that the method further comprises a step of requesting the location registration to the mobile station by the synchronized BTS before performing said step of performing the location registration of the mobile station.
According to the third embodiment, it is preferable that the inter-MSC soft handoff is performed by a router; the router connects the two neighboring BTSs, and the two BTSs are controlled by different respective MSCs.
It is preferable that said step of completing the call of the mobile station is performed after the completion of the inter-MSC soft handoff.
It is also preferable that said step of completing the call of the mobile station is performed during the period that the inter-MSC soft handoff is performed.